This invention relates to printing machines.
The invention finds application, for example, in forming print impressions of a printing plate on a sheet wherein the plate is removably mounted in the machine for a limited printing run, typically for a single operation of the machine.
One example of such a printing machine, described in U.K. Patent Specification No. 1,240,418, is a credit card imprinter, where the printing plate comprises an embossed card of plastics material. The imprinter provides a support member and a printing carriage slidable therealong. The credit card is placed at a predetermined location on the support member and a sales voucher, usually comprising three sheets of specially-prepared paper, is placed along the support member so as to extend over at least the embossed portion of the credit card. A so-called "dealer plate" is permanently mounted on the support member and bears embossed information identifying the vendor. The sales voucher is arranged also to overlie the dealer plate. The printer carriage is manually moved along the support member from a starting position and a roller thereof effects printing on the voucher of the information embossed on the card and dealer plate.
It has been found in some instances with such imprinters that sales vouchers have had the dealer plate information but not the credit card information printed thereon after a printing movement of the carriage, and that this has been due to inadvertent failure of the imprinter operator to insert the credit card on the support member. In other instances, the lack of printing has been due to incorrect insertion of the card, for example such that the embossed portion thereof does not underlie the voucher. If this omission is not corrected by a further imprinting oepration with the card in place, a financial loss will be incurred by the vendor.
It is an object of the present invention to provide a printing machine in which inadvertent incomplete printing, or any inadvertent printing, of a printing sheet is substantially prevented.